1. Field of the Invention
The present invention relates to an artificial snowseed and to a method for making artificial snow. More particularly, the present invention relates to an artificial, spherical, granular snowseed of a super water-absorbing polymer which retains the original spherical form after absorption of water without sticking to each other. The spherical snowseed may be of a dry or a water-swollen form. The snowseed can be used for making artificial snow having an appearance of granules or rice-flour cakes by freezing. The resulting artificial snow exhibits good properties for gliding on skis over the slope covered with such snow, and the snow conditions may be properly adjusted to skiing.
2. Background Art
(Natural snow)
There have recently been a marked decrease in snowfall and an accumulation of snow. As a result, the opening of many ski resorts is often hindered. In addition, in order to prepare a well-groomed packed ski slope, the natural snow on ski slopes requires frequent packing by a tracksetter because newly fallen natural snow is too soft and not suitable for smooth gliding on skis. On the other hand, the snow conditions on a tracksetter-groomed trail is not still suitable for a ski racing event, and the trail has to be groomed by treading it underfoot, followed by spraying water on the spread snow.
The slopes recreated by such means are very susceptible to the outside air temperature, and the quality of the snow varies widely from compact to corn with the passage of time. This is caused by sublimation and condensation of water molecules inside the snow layer thereby causing a change in the structure of snow crystals. It is not easy for skiers to glide smoothly on skis over slopes covered with corn snow; thus frequent snow-grooming, e.g. breaking the frozen crust is indispensable. These attempts are, however, still unsuccessful in giving a satisfactory results.
(Artificial snow)
Installation of snow machines has been popular in many skiing resorts to prolong the overall skiing season. Snow machines fall into two groups consisting mainly of a "gun" type and a "fan" type. A method of making artificial snow by snow machines comprises atomizing compressed water into a subzero atmosphere to make fine ice particles with the aid of adiabatic expansion of compressed air or the aid of cold air. The artificial snow thus produced contains 10% by weight or more of water, and has a density of about 0.3 to about 0.4 g/cm.sup.3, and a mechanical strength of less than 1 kg/cm.sup.2. The slope covered with such artificial snow is not suitable for skiing without being packed. Such artificial snow changes in quality more frequently than natural snow, and in certain cases, forms corn snow having an average outer diameter of about 1 to 5 mm in a few days. Corn snow is troublesome for skiers; and hence a measure similar to those as described above is necessary to overcome the accompanying problems.
A snow machine capable of shattering ice blocks by means of physical shock to make ice granules or snow flakes is also currently in use; however it is only capable of producing ice shavings or corn snow, and it is necessary to take measures to cope with the problems as described above.
Japanese Patent Publication No.63-500526 discloses a method for making artificial snow, which comprises mixing the granules of a water-swellable material, i.e. water-absorbing polymer with water, and aerating the water-swollen granules to the air, followed by freezing. The snow thus produced, has an appearance of fine stiff ice, like "EISBAHN", rather than snow, and has a density of about 0.4 to 0.9 g/cm.sup.3 with a mechanical strength of about 10 to several 100 kg/cm.sup.2, because these properties are highly susceptible to the aerating or freezing conditions. When shattered by means of physical shock to make granular ice or snow flakes, such "Eisbahn"-shaped stiff ice produces only corn snow. Therefore, in order to make artificial snow suitable for covering ski slopes by using the above water-swellable material alone, addition of a surfactant, regulation of the particle size and the water content of snow as well as frequent grooming of the slopes are indispensable to prevent the frozen snow particles from further agglomeration. Such snow is too difficult to handle for ski hill operators.
As the snow conditions on outdoor slopes are highly susceptible to the weather, indoor ski resorts that can be opened the year around have recently become popular. Artificial indoor ski slopes are laid with the foregoing artificial snow, artificial ice granules, snow flakes, or artificial snow made from a water-swellable material, e,g. a water-absorbing polymer and water; however the aforesaid problems still remain unsolved in these artificial indoor ski slopes.
Another indoor ski slope is produced by laying a floor with a paste comprising the aforesaid water-swellable material, e.g. water-absorbing polymer and water (blending weight ratio=about 1/80 to 1/100), followed by refrigerating the whole floor to create a surface similar to those of skating rinks. The surface is thereafter groomed while scraping off the surface ice to make artificial snow on top of an ice bed. In addition to the aforesaid problems, indoor ski slopes created in this way have an inherent problem in that pole plant is not easy because there is an ice layer, like "Eisbahn", beneath the artificial snow.
The aforesaid problems can be solved by employing the artificial snow made by refrigerating a water-swollen, super absorbing polymer (Japanese Patent Laid-Open Application Nos. 4-43274 and 4-43275 to the applicant of the invention). The artificial snow is provided in the form of frozen granules of a water-swollen super absorbing polymer itself or in the form of ice crystals similar to ice needles or frost columns (see FIG. 2) which are formed from the water released by the swollen granules upon cooling. In this case, the kinematic friction factor (.mu.k) increases unpreferably to about 0.04 to 0.10, compared to about 0.02 to 0.05 for natural powdery snow, as a result of the contact of the ski base with the granules. When the kinematic friction (.mu.k) factor is 0.06 or more, it becomes hard to control skis, e.g. to turn, because of the slowing-down of speed. It gives a sense of incongruity, and spoils pleasure in gliding.
Some of the problems associated with natural snow or conventional artificial snow for use in creating a ski slope include the following: i) It is not easy to freely adjust the snow density or strength so that it matches the particular skill or preference of skier. ii) Snow conditions vary widely over the slope with the passage of time; therefore it is hard to maintain the snow quality at its optimum. iii) Investment and maintenance costs are too high. iv) Conventional artificial snow made from a water-swellable material (water-absorbing polymer) and water by freezing is provided as ice blocks which should be further shattered for use. v) High kinematic friction factor (.mu.k).
It is accordingly an object of the present invention to provide artificial snow which has a kinematic friction factor (.mu.k) similar to that of natural powdery snow and good properties for gliding over on skis, and to provide an artificial snowseed for making such snow.